U.S. patent application number 16/770617 was filed with the patent office on 2020-10-01 for multilayer electrical steel sheet.
This patent application is currently assigned to JFE STEEL CORPORATION. The applicant listed for this patent is JFE STEEL CORPORATION. Invention is credited to Tatsuhiko HIRATANI, Yoshihiko ODA, Yoshiaki ZAIZEN.
Application Number | 20200308676 16/770617 |
Document ID | / |
Family ID | 1000004952951 |
Filed Date | 2020-10-01 |
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United States Patent
Application |
20200308676 |
Kind Code |
A1 |
ZAIZEN; Yoshiaki ; et
al. |
October 1, 2020 |
MULTILAYER ELECTRICAL STEEL SHEET
Abstract
Provided is a multilayer electrical steel sheet having both low
high-frequency iron loss and high magnetic flux density. The
multilayer electrical steel sheet has an inner layer and surface
layers provided on both sides of the inner layer, in which the
surface layers and the inner layer have a predetermined chemical
composition, the multilayer electrical steel sheet having:
.DELTA.Si of 0.5 mass % to 4.0 mass %; .DELTA.Al of 0.05 mass % or
less; a ratio of ti to t represented by ti/t of from 0.10 to 0.70;
a magnetic flux density Bio of 1.3 T or more; and a ratio of
B.sub.1 to B.sub.10 represented by B.sub.1/B.sub.10 of 0.45 or
more; and an iron loss W.sub.10/1k in W/kg and the sheet thickness
t in mm satisfy the following formula (1):
W.sub.10/1k.ltoreq.15+140.times.t (1).
Inventors: |
ZAIZEN; Yoshiaki;
(Chiyoda-ku, Tokyo, JP) ; ODA; Yoshihiko;
(Chiyoda-ku, Tokyo, JP) ; HIRATANI; Tatsuhiko;
(Chiyoda-ku, Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JFE STEEL CORPORATION |
Chiyoda-ku, Tokyo |
|
JP |
|
|
Assignee: |
JFE STEEL CORPORATION
Chiyoda-ku, Tokyo
JP
|
Family ID: |
1000004952951 |
Appl. No.: |
16/770617 |
Filed: |
December 10, 2018 |
PCT Filed: |
December 10, 2018 |
PCT NO: |
PCT/JP2018/045357 |
371 Date: |
June 8, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 38/06 20130101;
C22C 2204/00 20130101; C22C 38/002 20130101; C22C 2202/02 20130101;
C22C 38/12 20130101; C22C 38/008 20130101; C22C 38/02 20130101 |
International
Class: |
C22C 38/02 20060101
C22C038/02; C22C 38/00 20060101 C22C038/00; C22C 38/06 20060101
C22C038/06; C22C 38/12 20060101 C22C038/12 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2017 |
JP |
2017-238063 |
Claims
1. A multilayer electrical steel sheet comprising an inner layer
and surface layers provided on both sides of the inner layer,
wherein each of the surface layers has a chemical composition
containing, in mass %, Si: 2.5% to 6.0% and at least one selected
from the group consisting of P: 0.01% to 0.1%, Sn: 0.001% to 0.1%
and Sb: 0.001% to 0.1%, with the balance being Fe and inevitable
impurities, the inner layer has a chemical composition containing,
in mass %, Si: 1.5% to 5.0% and at least one selected from the
group consisting of P: 0.01% to 0.1%, Sn: 0.001% to 0.1% and Sb:
0.001% to 0.1%, with the balance being Fe and inevitable
impurities, and the multilayer electrical steel sheet has:
.DELTA.Si of 0.5 mass % to 4.0 mass %, .DELTA.Si being defined as a
difference between a Si content in each of the surface layers
[Si].sub.1 and a Si content in the inner layer [Si].sub.0
represented by [Si].sub.1-[Si].sub.0; .DELTA.Al of 0.05 mass % or
less, .DELTA.Al being defined as an absolute value of a difference
between a content of Al contained as an inevitable impurity in each
of the surface layers [Al].sub.1 and a content of Al contained as
an inevitable impurity in the inner layer [Al].sub.0 represented by
|[Al].sub.1-[Al].sub.0|; a ratio of t.sub.1 to t represented by
t.sub.1/t of from 0.10 to 0.70, where t.sub.1 denotes a total
thickness of the surface layers and t denotes a sheet thickness of
the multilayer electric steel sheet; B.sub.10 of 1.3 T or more,
where B.sub.10 denotes a magnetic flux density at a magnetic field
intensity of 1000 A/m; a ratio of B.sub.1 to B.sub.10 represented
by B.sub.1/B.sub.10 of 0.45 or more, where B.sub.1 denotes a
magnetic flux density at a magnetic field intensity of 100 A/m; and
an iron loss at a frequency of 1 kHz and a largest magnetic flux
density of 1.0 T represented by W.sub.10/1k in W/kg and the sheet
thickness t in mm satisfy the following formula (1):
W.sub.10/1k.ltoreq.15+140.times.t (1)
2. The multilayer electrical steel sheet according to claim 1,
wherein at least one of the chemical composition of each of the
surface layers or the chemical composition of the inner layer
further contains, in mass %, Mo: 0.001% to 0.1%.
Description
TECHNICAL FIELD
[0001] This disclosure relates to a multilayer electrical steel
sheet, and in particular, a multilayer electrical steel sheet
having both low high-frequency iron loss and high magnetic flux
density.
BACKGROUND
[0002] Motors for hybrid electric vehicles and cleaners are driven
in a high-frequency region such as 400 Hz to 2 kHz from the
viewpoint of reducing the size and achieving high efficiency.
Therefore, for non-oriented electrical steel sheets used for core
materials of such motors, electrical steel sheets having low
high-frequency iron loss and high magnetic flux density are
demanded.
[0003] To reduce the high-frequency iron loss, it is effective to
increase specific resistance. Therefore, high-Si steel having
increased specific resistance through the increase in the Si
content has been developed. However, since Si is a non-magnetic
element, the increase in the Si content leads to lower saturation
magnetization.
[0004] Therefore, as means for achieving both high-frequency iron
loss reduction and high magnetic flux density, gradient Si magnetic
materials having controlled Si concentration gradient in a
thickness direction of electrical steel sheets have been developed.
For example, JP H11-293422 A (PTL 1) proposes an electrical steel
sheet having a Si concentration gradient in a thickness direction
in which the Si concentration in a surface of the steel sheet is
higher than that of a mid-thickness part of the steel sheet.
Specifically, the electrical steel sheet has a mid-thickness part
with a Si concentration of 3.4% or more while having, on its both
surfaces, surface layers with a Si concentration of 5 mass % to 8
mass %. Further, the thickness of the surface layers is 10% or more
of the sheet thickness.
CITATION LIST
Patent Literature
[0005] PTL 1: JP H11-293422 A
SUMMARY
Technical Problem
[0006] However, when conventional gradient Si magnetic materials as
proposed in PTL 1 are used as the iron core materials of electric
appliances whose highest frequency is several kHz, the hysteresis
loss is high and thus the iron loss is not sufficiently
reduced.
[0007] It could thus be helpful to provide a multilayer electrical
steel sheet having both low high-frequency iron loss and high
magnetic flux density.
Solution to Problem
[0008] The inventors made intensive studies of a method of solving
the problem, and as a result, found that in order to reduce
high-frequency iron loss, it is important to suitably control the
difference in Si concentration between surface layers and an inner
layer of a steel sheet and add at least one selected from the group
consisting of P, Sn, and Sb. This disclosure is based on the above
finding and has the following primary features.
[0009] 1. A multilayer electrical steel sheet comprising an inner
layer and surface layers provided on both sides of the inner layer,
wherein
[0010] each of the surface layers has a chemical composition
containing (consisting of), in mass %, [0011] Si: 2.5% to 6.0% and
[0012] at least one selected from the group consisting of P: 0.01%
to 0.1%, Sn: 0.001% to 0.1% and Sb: 0.001% to 0.1%, with the
balance being Fe and inevitable impurities,
[0013] the inner layer has a chemical composition containing
(consisting of), in mass %, [0014] Si: 1.5% to 5.0% and [0015] at
least one selected from the group consisting of P: 0.01% to 0.1%,
Sn: 0.001% to 0.1% and Sb: 0.001% to 0.1%, with the balance being
Fe and inevitable impurities, and
[0016] the multilayer electrical steel sheet has: [0017] .DELTA.Si
of 0.5 mass % to 4.0 mass %, .DELTA.Si being defined as a
difference between a Si content in each of the surface layers
[Si].sub.1 and a Si content in the inner layer [Si].sub.0
represented by [Si].sub.1-[Si].sub.0; [0018] .DELTA.Al of 0.05 mass
% or less, .DELTA.Al being defined as an absolute value of a
difference between a content of Al contained as an inevitable
impurity in each of the surface layers [Al].sub.1 and a content of
Al contained as an inevitable impurity in the inner layer
[Al].sub.0 represented by |[Al].sub.1-[Al].sub.0|; [0019] a ratio
of t.sub.1 to t represented by t.sub.1/t of from 0.10 to 0.70,
where t.sub.1 denotes a total thickness of the surface layers and t
denotes a sheet thickness of the multilayer electric steel sheet;
[0020] B.sub.10 of 1.3 T or more, where B.sub.10 denotes a magnetic
flux density at a magnetic field intensity of 1000 A/m; [0021] a
ratio of B.sub.1 to B.sub.10 represented by B.sub.1/B.sub.10 of
0.45 or more, where B.sub.1 denotes a magnetic flux density at a
magnetic field intensity of 100 A/m; and [0022] an iron loss at a
frequency of 1 kHz and a largest magnetic flux density of 1.0 T
represented by W.sub.10/1k in W/kg and the sheet thickness t in mm
satisfy the following formula (1):
[0022] W.sub.10/1k.ltoreq.15+140.times.t (1).
[0023] 2. The multilayer electrical steel sheet according to 1.,
wherein at least one of the chemical composition of each of the
surface layers or the chemical composition of the inner layer
further contains, in mass %, Mo: 0.001% to 0.1%.
Advantageous Effect
[0024] According to this disclosure, it is possible to provide a
multilayer electrical steel sheet having both low high-frequency
iron loss and high magnetic flux density.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] In the accompanying drawings:
[0026] FIG. 1 is a schematic diagram illustrating the structure of
a multilayer electrical steel sheet according to one of the
embodiments of this disclosure;
[0027] FIGS. 2A and 2B are schematic diagrams illustrating examples
of the Si content profile in a thickness direction of the
multilayer electrical steel sheet;
[0028] FIG. 3 is a graph illustrating a correlation between the
difference in Si content between surface layers and an inner layer
(.DELTA.Si) and the total iron loss (W.sub.10/1k);
[0029] FIG. 4 is a graph illustrating a correlation between the
difference in Si content between the surface layers and the inner
layer (.DELTA.Si) and the magnetic flux density ratio (B
i/B.sub.10); and
[0030] FIG. 5 is a graph illustrating a correlation between the
multilayer ratio defined as a ratio of a total thickness of the
surface layers t.sub.1 to the sheet thickness of the multilayer
electrical steel sheet t and the total iron loss (W.sub.10/1k).
DETAILED DESCRIPTION
[0031] Detailed description is given below. The following
description merely presents examples of preferred embodiments of
this disclosure, and this disclosure is not limited to these
embodiments.
[0032] [Multilayer Electrical Steel Sheet]
[0033] FIG. 1 is a schematic diagram illustrating the structure of
a multilayer electrical steel sheet according to one of the
embodiments of this disclosure. Further, FIGS. 2A and 2B are
schematic diagrams illustrating examples of the Si content profile
in a thickness direction of the multilayer electrical steel sheet.
In FIGS. 2A and 2B, the vertical axis indicates a position in the
thickness direction, 0 denotes one surface of the multilayer
electrical steel sheet, and t denotes the other surface of the
multilayer electrical steel sheet.
[0034] As illustrated in FIG. 1, a multilayer electrical steel
sheet 1 of this disclosure (hereinafter, also referred to simply as
"steel sheet") has an inner layer 10 and surface layers 20 provided
on both sides of the inner layer 10, the inner layer 10 and the
surface layers 20 having different Si contents. The Si content may
change continuously (FIG. 2A) or stepwise (FIG. 2B) in the
thickness direction of the steel sheet. When the Si content changes
stepwise, it may change in two or more steps. In the following
description, the "surface layers" indicate surface layers provided
on the surfaces of both sides of the multilayer electrical steel
sheet. Therefore, in this disclosure, both a first surface layer
provided on one surface of the multilayer electrical steel sheet
and a second surface layer provided on the other surface of the
multilayer electrical steel sheet satisfy the conditions described
below.
[0035] A part having a higher Si content than an average of Si
contents over the total sheet thickness of the steel sheet is
defined as a "surface layer" and a part having a lower Si content
than the average is defined as an "inner layer". As described
below, when the multilayer electrical steel sheet is manufactured
by cladding two types of steel materials having different Si
contents (high Si material and low Si material) with each other,
typically, a part made of the high Si material is a surface layer
and a part made of the low Si material is an inner layer. In this
case, the Si content in each of the surface layers is substantially
constant and the Si content in the inner layer is also
substantially constant.
[0036] [Chemical Composition]
[0037] First, the chemical compositions of each of the surface
layers and the inner layer are described. When components are
expressed in "%", this refers to "mass %" unless otherwise
stated.
[0038] [Chemical Composition of Surface Layer]
[0039] First, the chemical composition of each of the surface
layers will be described. In this disclosure, both the first
surface layer provided on one surface of the multilayer electrical
steel sheet and the second surface layer provided on the other
surface of the multilayer electrical steel sheet have the chemical
composition described below. The chemical composition of the first
surface layer and the chemical composition of the second surface
layer may be typically the same but may be different from each
other. Further, the content of an element in each of the surface
layers indicates an average content of the element in each surface
layer.
[0040] Si: 2.5% to 6.0%
[0041] Si is an element having an effect of increasing the
electrical resistance of the steel sheet and reducing eddy current
loss. When the Si content in each of the surface layers
([Si].sub.1) is less than 2.5%, the eddy current loss cannot be
effectively reduced. Therefore, the Si content in each of the
surface layers is set to 2.5% or more, preferably 3.0% or more, and
more preferably more than 3.5%. On the other hand, when the Si
content in each of the surface layers is more than 6.0%, the
magnetic flux density decreases due to lower saturation
magnetization. Therefore, the Si content in each of the surface
layers is set to 6.0% or less, preferably less than 5.5%, and more
preferably 5.0% or less. As described above, a Si content of 2.5%
to 6.0% in each of the surface layers means that the average Si
content in the first surface layer is 2.5% to 6.0% and the average
Si content in the second surface layer is 2.5% to 6.0%. The average
Si content in the first surface layer may be the same with or
different from the average Si content in the second surface layer.
The same definition applies to other elements.
[0042] The chemical composition in each of the surface layers
further contains at least one selected from the group consisting of
P: 0.01% to 0.1%, Sn: 0.001% to 0.1%, and Sb: 0.001% to 0.1%.
[0043] P: 0.01% to 0.1%
[0044] The addition of P greatly improves the texture, which makes
it possible to improve the magnetic flux density and lower the
hysteresis loss. When P is added, to obtain this effect, the P
content is set to 0.01% or more. On the other hand, a P content
exceeding 0.1% causes saturation of the effect and additionally,
lowers the manufacturability and increases the cost. Therefore, the
P content is set to 0.1% or less.
[0045] Sn: 0.001% to 0.1%
[0046] As with P, the addition of Sn greatly improves the texture,
which makes it possible to improve the magnetic flux density and
lower the hysteresis loss. When Sn is added, to obtain this effect,
the Sn content is set to 0.001% or more. On the other hand, a Sn
content exceeding 0.1% causes saturation of the effect and
additionally, lowers the manufacturability and increases the cost.
Therefore, the Sn content is set to 0.1% or less.
[0047] Sb: 0.001% to 0.1%
[0048] As with P and Sn, the addition of Sb greatly improves the
texture, which makes it possible to improve the magnetic flux
density and lower the hysteresis loss. When Sb is added, to obtain
this effect, the Sb content is set to 0.001% or more. On the other
hand, a Sb content exceeding 0.1% causes saturation of the effect
and additionally, lowers the manufacturability and increases the
cost. Therefore, the Sb content is set to 0.1% or less.
[0049] In one embodiment of this disclosure, each of the surface
layers has a chemical composition containing the above elements
with the balance being Fe and inevitable impurities.
[0050] Examples of elements which may be contained as the
inevitable impurities in the multilayer electrical steel sheet
include Al. When the Al content is limited to 0.1% or less, the
magnetic flux density can be further improved. Therefore, the Al
content is preferably limited to 0.1% or less.
[0051] Further, in another embodiment of this disclosure, the
chemical composition of each of the surface layers may further
contain Mo in an amount described below.
[0052] Mo: 0.001% to 0.1%
[0053] Mo is an element having an effect of suppressing the
oxidation of the surface layers of the steel sheet to thereby
further reduce iron loss. When Mo is added, to obtain this effect,
the Mo content is set to 0.001% or more. On the other hand, when
the Mo content exceeds 0.1%, carbides are formed, leading to an
increase in iron loss. Therefore, the Mo content is set to 0.1% or
less.
[0054] Each of the surface layers according to one embodiment of
this disclosure may have a chemical composition containing, in mass
%,
[0055] Si: 2.5% to 6.0%,
[0056] at least one selected from the group consisting of P: 0.01%
to 0.1%, Sn: 0.001% to 0.1%, and Sb: 0.001% to 0.1%, and
[0057] optionally, Mo: 0.001% to 0.1%, with the balance being Fe
and inevitable impurities.
[0058] Further, each of the surface layers according to another
embodiment of this disclosure may have a chemical composition
containing, in mass %,
[0059] Si: 2.5% to 6.0%,
[0060] at least one selected from the group consisting of P: 0.01%
to 0.1%, Sn: 0.001% to 0.1%, and Sb: 0.001% to 0.1%, and
[0061] optionally, Mo: 0.001% to 0.1%, with the balance being Fe
and inevitable impurities.
[0062] [Chemical Composition of Inner Layer]
[0063] Next, the chemical composition of the inner layer will be
described. The content of an element in the inner layer indicates
an average content of the element in the inner surface.
[0064] Si: 1.5% to 5.0%
[0065] A Si content in the inner layer ([Si].sub.0) of less than
1.5% causes an increase in high-frequency iron loss. Therefore, the
Si content of the inner layer is set to 1.5% or more. On the other
hand, a Si content in the inner layer of more than 5.0% causes
cracking of a motor core in punching the core. Therefore, the Si
content in the inner layer is set to 5.0% or less. The Si content
in the inner layer is preferably set to 4.0% or less and more
preferably 2.8% or less.
[0066] The chemical composition in the inner layer further contains
at least one selected from the group consisting of P: 0.01% to
0.1%, Sn: 0.001% to 0.1%, and Sb: 0.001% to 0.1%.
[0067] P: 0.01% to 0.1%
[0068] The addition of P greatly improves the texture, which makes
it possible to improve the magnetic flux density and lower the
hysteresis loss. When P is added, to obtain this effect, the P
content is set to 0.01% or more. On the other hand, a P content
exceeding 0.1% causes saturation of the effect and additionally,
lowers the manufacturability and increases the cost. Therefore, the
P content is set to 0.1% or less.
[0069] Sn: 0.001% to 0.1%
[0070] As with P, the addition of Sn greatly improves the texture,
which makes it possible to improve the magnetic flux density and
lower the hysteresis loss. When Sn is added, to obtain this effect,
the Sn content is set to 0.001% or more. On the other hand, a Sn
content exceeding 0.1% causes saturation of the effect and
additionally, lowers the manufacturability and increases the cost.
Therefore, the Sn content is set to 0.1% or less.
[0071] Sb: 0.001% to 0.1%
[0072] As with P and Sn, the addition of Sb greatly improves the
texture, which makes it possible to improve the magnetic flux
density and lower the hysteresis loss. When Sb is added, to obtain
this effect, the Sb content is set to 0.001% or more. On the other
hand, a Sb content exceeding 0.1% causes saturation of the effect
and additionally, lowers the manufacturability and increases the
cost. Therefore, the Sb content is set to 0.1% or less.
[0073] In one embodiment of this disclosure, the inner layer has a
chemical composition containing the above elements with the balance
being Fe and inevitable impurities.
[0074] Examples of elements which can be contained as the
inevitable impurities in the multilayer electrical steel sheet
include Al. When the Al content is limited to 0.1% or less, the
magnetic flux density can be further improved. Therefore, the Al
content is preferably limited to 0.1% or less.
[0075] Further, in another embodiment of this disclosure, the
chemical composition of the inner layer may further contain Mo in
an amount described below.
[0076] Mo: 0.001% to 0.1%
[0077] As described above, Mo is an element having an effect of
suppressing the oxidation of the surface layers of the steel sheet
to thereby further reduce iron loss. To prevent the oxidation, it
suffices that Mo exists in the surface layers of the steel sheet,
but Mo may be added to the inner layer. For example, when the
multilayer electrical steel sheet is manufactured by a siliconizing
treatment as described below, in order to add Mo to the surface
layers, it suffices to add Mo to the entire steel sheet and in this
case, Mo also exists in the inner layer. Further, even the
multilayer electrical steel sheet is manufactured by a method other
than the siliconizing treatment, Mo may be added to the inner
layer. From the viewpoint of manufacture, when Mo is added to the
inner layer, the Mo content in the inner layer is set to 0.001% or
more as with the Mo content in each of the surface layers. On the
other hand, when the Mo content exceeds 0.1%, carbides are formed,
leading to an increase in iron loss. Therefore, the Mo content is
set to 0.1% or less.
[0078] The inner layer according to one embodiment of this
disclosure may have a chemical composition containing, in mass
%,
[0079] Si: 1.5% to 5.0%,
[0080] at least one selected from the group consisting of P: 0.01%
to 0.1%, Sn: 0.001% to 0.1%, and Sb: 0.001% to 0.1%, and
[0081] optionally, Mo: 0.001% to 0.1%, with the balance being Fe
and inevitable impurities.
[0082] Further, the inner layer according to another embodiment of
this disclosure may have a chemical composition containing, in mass
%,
[0083] Si: 1.5% to 5.0%,
[0084] at least one selected from the group consisting of P: 0.01%
to 0.1%, Sn: 0.001% to 0.1%, and Sb: 0.001% to 0.1%, and
[0085] optionally, Mo: 0.001% to 0.1%, with the balance being Fe
and inevitable impurities.
[0086] [Difference in Si Content]
[0087] To examine the effect of the difference in Si content
between the surface layers and the inner layer (.DELTA.Si) on the
magnetic properties, multilayer electrical steel sheets having
different .DELTA.Si were manufactured by the following procedures
and the magnetic properties were evaluated.
[0088] First, steel for the surface layers was attached to both
surfaces of steel for the inner layer so that the ratio of the
thickness of the surface layers to the sheet thickness (total
thickness) of the multilayer electrical steel sheet was 0.30 and
subjected to hot rolling to obtain a hot-rolled steel sheet. Each
of the steel for the surface layers and the steel for the inner
layer was melted so as to obtain a desired chemical composition to
prepare an ingot. The Si content in the inner layer [Si].sub.0 was
set to 2.0% and the Si content in each of the surface layers
[Si].sub.1 was changed in the range of 2.1% to 6.5%. The Al content
was set to 0.001% and the Sn content was set to 0.04% in both the
surface layers and the inner layer. The chemical compositions of
each of the surface layers and the inner layer had the balance of
Fe and inevitable impurities. The surface layers on both surfaces
had the same chemical composition.
[0089] After the hot rolling, the hot-rolled steel sheet was
subjected to hot-rolled sheet annealing of 950.degree. C..times.30
s, followed by cold rolling to obtain a cold-rolled steel sheet
having a sheet thickness of 0.20 mm. Subsequently, the cold-rolled
steel sheet was subjected to final annealing of 1000.degree.
C..times.30 s to obtain a multilayer electrical steel sheet.
[0090] A test piece having a width of 30 mm and a length of 180 mm
was collected from the obtained multilayer electrical steel sheet
and subjected to the Epstein test to evaluate the magnetic
properties. In the Epstein test, an L-direction test piece
collected so that the length direction of the test piece was
parallel to the rolling direction (L direction) and a C-direction
test piece collected so that the length direction of the test piece
was parallel to the direction orthogonal to the rolling direction
(C direction) were used in equal amounts to measure the averages of
the magnetic properties in the L direction and the C direction.
[0091] FIG. 3 indicates a correlation between .DELTA.Si (mass %)
and the total iron loss at 1.0 T and 1 kHz represented by
W.sub.10/1k (W/kg), .DELTA.Si being defined as a difference in Si
content between each of the surface layers and the inner layer
([Si].sub.1-[Si].sub.0). Further, FIG. 4 indicates a correlation
between .DELTA.Si and the magnetic flux density ratio. The
"magnetic flux density ratio" indicates the ratio of B.sub.1 to
B.sub.10 represented by B.sub.1/B.sub.10, where B.sub.1 denotes a
magnetic flux density at a magnetic field intensity of 100 A/m and
B.sub.10 denotes a magnetic flux density at a magnetic field
intensity of 1000 A/m.
[0092] As can be seen from the results illustrated in FIG. 3, when
.DELTA.Si is 0.5 mass % or more and 4.0 mass % or less, the iron
loss can be reduced to low. Further, as can be seen from the
results illustrated in FIG. 4, when .DELTA.Si exceeds 4.0 mass %,
the magnetic flux density ratio is suddenly lowered. This is
believed to be because of the following reasons. Specifically, when
the Si content in each of the surface layers is higher than that in
the inner layer, the magnetic permeability of each of the surface
layers is higher than that of the inner layer. As a result,
magnetic fluxes concentrate to the surface layer, lowering the eddy
current loss. However, when .DELTA.Si is excessively large, the
difference in lattice constant and the difference in
magnetostriction between each of the surface layers and the inner
layer become large. As a result, since the stress applied during
the magnetization of the steel sheet is increased, the hysteresis
loss increases and the magnetic flux density decreases in low and
middle magnetic field ranges.
[0093] For the above reasons, in this disclosure, .DELTA.Si defined
as a difference between the Si content in each of the surface
layers and the Si content in the inner layer
([Si].sub.1-[Si].sub.0) is set to 0.5 mass % to 4.0 mass %.
[0094] [Difference in Al Content]
[0095] Although the magnetostriction in the surface layers and the
inner layer is strongly influenced by the Si content, it is also
influenced by the texture. For example, since the formation of the
texture greatly varies during final annealing when the amount of
impurities is different between the surface layers and the inner
layer, the difference in magnetostriction between the surface
layers and the inner layer becomes large. In particular, Al is an
element which greatly influences the formation of the texture.
Therefore, .DELTA.Al is set to 0.05 mass % or less, where .DELTA.Al
is defined as an absolute value of the difference between the
content of Al contained as an inevitable impurity in each of the
surface layers [Al].sub.1 and the content of Al contained as an
inevitable impurity in the inner layer [Al].sub.0
(|[Al].sub.1-[Al].sub.0|). On the other hand, no lower limit is
placed on .DELTA.Al, but .DELTA.Al may be 0.
[0096] [Multilayer Ratio]
[0097] Next, to examine the effect of the ratio of the total
thickness of the surface layers t.sub.1 to the sheet thickness of
the multilayer electrical steel sheet t (tilt) (hereinafter, also
referred to as "multilayer ratio") on the magnetic properties,
multilayer electrical steel sheets having different multilayer
ratios were manufactured by the following procedures and the
magnetic properties were evaluated. The "total thickness of the
surface layers" indicates the sum of the thicknesses of the surface
layers provided on both sides.
[0098] First, steel for the surface layers and steel for the inner
layer were attached with each other so as to obtain a multilayer
ratio of 0.02 to 0.80 and subjected to hot rolling to obtain a
hot-rolled steel sheet. Each of the steel for the surface layers
and the steel for the inner layer was melted so as to obtain a
desired chemical composition to prepare an ingot. The Si content in
each of the surface layers [Si].sub.0 was set to 4.5% and the Si
content in the inner layer [Si].sub.1 was set to 2.0%. Further,
both in each of the surface layers and in the inner layer, the P
content was set to 0.05%, the Sn content was set to 0.05%, the Sb
content and the content of Al contained as an inevitable impurity
were each set to 0.001%. The balance was Fe and inevitable
impurities. The surface layers on both surfaces had the same
chemical composition.
[0099] After the hot rolling, the hot-rolled steel sheet was
subjected to hot-rolled sheet annealing of 950.degree. C..times.30
s, followed by cold rolling to obtain a cold-rolled steel sheet
having a sheet thickness of 0.10 mm. Subsequently, the cold-rolled
sheet was subjected to final annealing of 1000.degree. C..times.30
s to obtain a multilayer electrical steel sheet.
[0100] FIG. 5 illustrates a correlation between the multilayer
ratio (tilt) and the total iron loss (W.sub.10/1k). From the
result, it is found that when the multilayer ratio is from 0.10 to
0.70, the iron loss is greatly reduced. The reduction in the iron
loss is believed to be because of the following reasons. First,
since the ratio of the surface layers which have high resistance is
low when the multilayer ratio is less than 0.10, the eddy current
which concentrates on the surface layers cannot be effectively
reduced. On the other hand, since the difference in magnetic
permeability between the surface layers and the inner layer is
small when the multilayer ratio is more than 0.70, the magnetic
flux penetrates to the inner surface and the eddy current loss also
occurs from the inner surface. Therefore, the iron loss can be
reduced by setting the multilayer ratio in a range of from 0.10 to
0.70. For the above reasons, the multilayer ratio (tilt) in this
disclosure is set to 0.10 to 0.70.
[0101] [Sheet Thickness]
[0102] The sheet thickness of the multilayer electrical steel sheet
t is not particularly limited and t may be any value. However, when
the multilayer electrical steel sheet is excessively thin, it is
difficult to perform cold rolling and annealing in manufacturing
the multilayer electrical steel sheet, which may cause an increase
in costs. Therefore, from the viewpoint of reducing the
manufacturing cost, t is preferably set to 0.03 mm or more. On the
other hand, when t is set to 0.3 mm or less, the eddy current loss
can be further reduced, and as a result, the total iron loss can be
further lowered. Therefore, t is preferably set to 0.3 mm or
less.
[0103] [Magnetic Flux Density]
B.sub.10: 1.3 T or More
[0104] The multilayer electrical steel sheet of this disclosure has
high magnetic flux density. Specifically, the magnetic flux density
at a magnetic field intensity of 1000 A/m represented by B.sub.10
is 1.3 T or more. Increasing the magnetic flux density in the
electrical steel sheet is effective for improving the torque of a
motor manufactured using the electrical steel sheet. Further, when
the magnetic flux density is high, the same torque can be obtained
with low current, and as a result, copper loss can be reduced.
[0105] B.sub.1/B.sub.10: 0.45 or More
[0106] The ratio of B.sub.1 to B.sub.10 represented by
B.sub.1/B.sub.10 is set to 0.45 or more, where B.sub.1 denotes a
magnetic flux density at a magnetic field intensity of 100 A/m. By
increasing B.sub.1/B.sub.10, a good rise can be obtained in a
magnetization curve in a designed magnetic flux density region used
in a small motor. Since this reduces a motor current required to
obtain a predetermined torque, the copper loss is reduced and thus,
the motor efficiency can be improved.
[0107] [Iron Loss]
[0108] In this disclosure, the iron loss at a frequency of 1 kHz
and a largest magnetic flux density of 1.0 T (total iron loss)
W.sub.10/1k (W/kg) and the sheet thickness tin mm need to satisfy
the following formula (1):
W.sub.10/1k.ltoreq.15+140.times.t (1).
[0109] The reason is that when the relation of the formula (1) is
not satisfied, an extremely large amount of heat is generated in
stator cores, significantly lowering the motor efficiency. Since
the iron loss depends on the sheet thickness, the upper limit of
the iron loss is defined in the formula (1), considering the effect
of the sheet thickness.
[0110] In the electrical steel sheet, when the magnetic flux
density is increased, the iron loss is typically increased.
Therefore, common motor cores are designed so that the magnetic
flux density is about 1.0 T. On the other hand, the multilayer
electrical steel sheet of this disclosure achieves both high
magnetic flux density and low iron loss which are conflicting
properties by controlling the chemical compositions of the surface
layers and the inner layer and the multilayer ratio of the steel
sheet as described above.
[0111] [Manufacturing Method]
[0112] The method of manufacturing the multilayer electrical steel
sheet of this disclosure is not particularly limited and may be any
method. Examples of the manufacturing method include a method of
cladding steel raw materials having different Si contents. The
chemical compositions of the steel raw materials can be adjusted
by, for example, blowing materials having different compositions in
a converter to obtain molten steel and subjecting the molten steel
to degassing treatment.
[0113] The cladding method is not particularly limited. However,
for example, a steel slab for the surface layers and a steel slab
for the inner layer each having the chemical composition described
above may be prepared and the steel slab for the surface layers may
be attached, with a thickness such that the eventual multilayer
ratio is a desired value, to both surfaces of the steel slab for
the inner layer, followed by rolling. The rolling may be, for
example, at least one selected from the group consisting of hot
rolling, warm rolling, and cold rolling. In general, the
combination of hot rolling and subsequent warm rolling or the
combination of hot rolling and subsequent cold rolling is
preferable. After the hot rolling, hot-rolled sheet annealing is
preferably performed. Further, the warm rolling and cold rolling
may be performed twice or more with intermediate annealing
performed therebetween. The rolling finish temperature and the
coiling temperature during the hot rolling are not particularly
limited and may be determined according to the conventional method.
After the rolling, final annealing is performed. The multilayer
electrical steel sheet obtained by cladding the steel materials
having different Si contents has the Si content profile as
illustrated in, for example, FIG. 2B.
[0114] As another manufacturing method, siliconizing treatment may
be used. When the siliconizing treatment is used, by subjecting a
steel sheet having a constant Si content in the thickness direction
to siliconizing treatment, the Si content in the surface layers on
both sides of the steel sheet can be increased. The method of the
siliconizing treatment is not particularly limited and may be any
method. For example, a method in which Si is deposited on the
surfaces of the steel sheet by a chemical vapor deposition method
(CVD method) and subsequently heat treatment is performed to
diffuse Si to the inside of the steel sheet can be used. The Si
contents of the surface layers and the inner layer can be
controlled by adjusting the amount of Si deposited by the CVD
method and heat treatment conditions. The multilayer electrical
steel sheet obtained by the siliconizing treatment has the Si
content profile as illustrated in, for example, FIG. 2A.
Examples
[0115] To determine the effect of this disclosure, multilayer
electrical steel sheets were manufactured in the following
procedures and their magnetic properties were evaluated.
[0116] First, for each multilayer electrical steel sheet, two types
of steel slabs for a surface layer and an inner layer having the
chemical compositions listed in Table 1 were prepared. Next, the
steel slab for a surface layer was stacked on both sides of the
steel slab for an inner layer. The outer periphery of the stacked
steel slabs was welded. Therefore, the surface layers on both sides
had the same chemical composition. The chemical compositions of the
steel slabs were adjusted by blowing the steel slabs in a converter
and subsequently subjecting them to degassing treatment. The
chemical compositions were maintained in the resulting multilayer
electrical steel sheet.
[0117] Next, the stacked steel slabs were heated at 1130.degree. C.
for 1 hr, and subsequently hot rolled to obtain a hot-rolled steel
sheet having a sheet thickness of up to 2.0 mm. The hot rolling
finish temperature in the hot rolling was set to 800.degree. C.
Then, the hot-rolled steel sheet was coiled at a coiling
temperature of 610.degree. C., and then subjected to hot-rolled
sheet annealing of 940.degree. C..times.30 s. Subsequently, the
hot-rolled steel sheet was subjected to pickling and cold rolling,
followed by annealing at a final annealing temperature listed in
Table 1 to obtain a multilayer electrical steel sheet. The sheet
thickness of the resulting multilayer electrical steel sheet t and
a ratio of a total thickness of the surface layers t.sub.1 to t
(i.e., a multilayer ratio) were as listed in Table 2.
[0118] For comparison, normal electrical steel sheets without
cladding were subjected to the same test (Nos. 1 and 2). These
electrical steel sheets as comparative examples had the same
chemical composition in the surface layers and the inner layer.
[0119] Further, the multilayer electrical steel sheet of No. 33 was
manufactured by a siliconizing method. Specifically, a cold-rolled
steel sheet having a Si content of 2.0% and a sheet thickness of
0.2 mm was subjected to siliconizing treatment at 1200.degree. C.
The average of Si contents over the total sheet thickness of the
steel sheet was calculated. A part having a higher Si concentration
than the average was defined as a surface layer and a part having a
lower Si concentration than the average was defined as an inner
layer. The Si content in each of the surface layers was an average
of Si contents in the surface layers. Further, listed as the
magnetostriction measurements of the surface layers and the inner
layer are the magnetostriction measurements of a steel sheet having
the same Si content as the average of Si contents and the same
chemical composition as that of the multilayer electrical steel
sheet of No. 33 except for the Si content.
[0120] (Magnetic Properties)
[0121] Next, each of the obtained multilayer electrical steel
sheets was measured for its magnetic properties. The measurement of
the magnetic properties was performed using a 25 cm Epstein frame
according to JIS C 2550-1. As the magnetic properties, the iron
loss at 1.0 T and 1 kHz represented by W.sub.10/1k (W/kg), the
magnetic flux density at a magnetic field intensity of 1000 A/m
represented by B.sub.10, and the magnetic flux density at a
magnetic field intensity of 100 A/m represented by B.sub.1 were
measured. The measurement results are as listed in Table 2.
[0122] As can be seen from the results of Tables 1 and 2, the
multilayer electrical steel sheets of our examples satisfying the
conditions of this disclosure had excellent properties, i.e., low
high-frequency iron loss and high magnetic flux density. Therefore,
the multilayer electrical steel sheets according to this disclosure
can be extremely suitably used as motor cores of hybrid electric
vehicles, electric vehicles, cleaners, high speed power generators,
air compressors, machine tools, and the like which are driven at
high frequencies, and further as core materials of transformers,
reactors, and the like.
TABLE-US-00001 TABLE 1 Chemical composition (mass %) Surface layer*
Inner layer* No. Si Al P Sn Sb Mo Si Al P Sn Sb Mo .DELTA.Si
.DELTA.Al 1 2.5 0.0010 0.05 0.0010 0.0010 0.0010 2.5 0.0010 0.05
0.0010 0.0010 0.0010 0.00 0.0000 2 5.5 0.0010 0.01 0.0400 0.0010
0.0010 5.5 0.0010 0.01 0.0400 0.0010 0.0010 0.00 0.0000 3 4.0
0.0010 0.04 0.0010 0.0010 0.0010 2.4 0.0005 0.04 0.0010 0.0010 --
1.60 0.0005 4 4.2 0.0010 0.04 0.0400 0.0010 0.0010 2.0 0.0010 0.04
0.0400 0.0010 -- 2.20 0.0000 5 4.7 0.0010 0.01 0.0600 0.0200 0.0010
2.5 0.0010 0.01 0.0600 0.0200 -- 2.20 0.0000 6 6.0 0.0020 0.03
0.0010 0.0010 0.0010 1.7 0.0010 0.03 0.0010 0.0010 0.0010 4.30
0.0010 7 4.0 0.0025 0.07 0.0300 0.0010 0.0010 1.2 0.0010 0.07
0.0300 0.0010 0.0010 2.80 0.0015 8 4.0 0.0030 -- -- -- 0.0010 2.0
0.0030 -- -- -- 0.0010 2.00 0.0000 9 4.3 0.0010 0.06 0.0400 0.0010
0.0010 1.9 0.0010 0.06 0.0400 0.0010 0.0010 2.40 0.0000 10 4.3
0.0010 0.01 0.0400 0.0300 0.0010 1.9 0.0010 0.01 0.0400 0.0300
0.0010 2.40 0.0000 11 4.3 0.0010 0.01 0.0010 0.0800 0.0010 1.9
0.0010 0.01 0.0010 0.0800 0.0010 2.40 0.0000 12 4.3 0.0010 0.05
0.0400 0.0010 0.0100 1.9 0.0010 0.05 0.0400 0.0010 0.0100 2.40
0.0000 13 4.5 0.0010 0.03 0.0300 0.0010 0.0010 2.1 0.0010 0.03
0.0300 0.0010 -- 2.40 0.0000 14 4.5 0.0010 0.03 0.0300 0.0010
0.0010 2.1 0.0010 0.03 0.0300 0.0010 -- 2.40 0.0000 15 4.5 0.0010
0.03 0.0300 0.0010 0.0010 2.1 0.0010 0.03 0.0300 0.0010 -- 2.40
0.0000 16 4.5 0.0010 0.03 0.0300 0.0010 0.0010 2.1 0.0010 0.03
0.0300 0.0010 0.0010 2.40 0.0000 17 4.2 0.0024 0.04 0.0400 0.0010
0.0030 2.2 0.0010 0.04 0.0400 0.0010 0.0030 2.00 0.0014 18 4.2
0.0600 0.04 0.0400 0.0010 0.0030 2.2 0.0010 0.04 0.0400 0.0010
0.0030 2.00 0.0590 19 4.1 0.0010 0.05 0.0400 0.0010 0.0010 2.5
0.0020 0.05 0.0400 0.0010 -- 1.60 0.0010 20 4.1 0.0010 0.01 0.0600
0.0010 0.0010 2.5 0.0020 0.01 0.0600 0.0010 -- 1.60 0.0010 21 4.1
0.0010 0.05 0.0400 0.0010 0.0010 2.5 0.0020 0.05 0.0400 0.0010 --
1.60 0.0010 22 4.1 0.0010 0.05 0.0010 0.0400 0.0010 2.5 0.0020 0.05
0.0010 0.0400 -- 1.60 0.0010 23 4.3 0.0010 0.01 0.0400 0.0300
0.0010 1.9 0.0020 0.01 0.0400 0.0300 -- 2.40 0.0010 24 4.3 0.0010
0.01 0.0600 0.0010 0.0010 1.9 0.0020 0.01 0.0600 0.0010 -- 2.40
0.0010 25 4.3 0.0010 0.01 0.0010 0.0700 0.0010 1.9 0.0020 0.01
0.0010 0.0700 -- 2.40 0.0010 26 4.3 0.0010 0.01 0.0400 0.0400
0.0010 1.9 0.0020 0.01 0.0400 0.0400 -- 2.40 0.0010 27 4.2 0.0010
0.06 -- -- -- 2.4 0.0010 0.06 -- -- -- 1.80 0.0000 28 4.2 0.0010 --
0.0500 -- -- 2.4 0.0010 -- 0.0500 -- -- 1.80 0.0000 29 4.2 0.0010
-- -- 0.0500 -- 2.4 0.0010 -- -- 0.0500 -- 1.80 0.0000 30 4.2
0.0010 0.05 0.0500 -- -- 2.4 0.0010 0.05 0.0500 -- -- 1.80 0.0000
31 5.8 0.0010 0.04 -- -- -- 3.5 0.0010 0.04 -- -- -- 2.30 0.0000 32
3.2 0.0010 -- 0.0400 -- -- 2.0 0.0010 -- 0.0400 -- -- 1.20 0.0000
33 4.5 0.0010 0.05 0.0500 -- -- 2.0 0.0010 0.05 0.0500 -- -- 2.50
0.0000 *The balance is Fe and inevitable impurities.
TABLE-US-00002 TABLE 2 Final Magnetic properties Sheet Multilayer
annealing Conditions thickness ratio temperature W.sub.10/1k of
B.sub.1 B.sub.10 No. t (mm) t.sub.1/t (.degree. C.) 15 + 140t
(W/kg) formula (1) (T) (T) B.sub.1/B.sub.10 Remarks 1 0.20 -- 1000
43 44.0 unsatisfied 1.10 1.51 0.73 Comparative Example 2 0.20 --
1000 43 38.0 satisfied 1.07 1.25 0.86 Comparative Example 3 0.25
0.30 1020 50 44.0 satisfied 1.10 1.48 0.74 Example 4 0.20 0.30 1000
43 37.5 satisfied 1.15 1.45 0.79 Example 5 0.20 0.30 1000 43 37.2
satisfied 1.02 1.44 0.71 Example 6 0.20 0.30 1050 43 44.0
unsatisfied 0.65 1.24 0.52 Comparative Example 7 0.15 0.30 1150 36
40.0 unsatisfied 1.15 1.54 0.75 Comparative Example 8 0.25 0.30
1000 50 51.0 unsatisfied 0.95 1.25 0.76 Comparative Example 9 0.20
0.30 1000 43 38.0 satisfied 1.15 1.50 0.77 Example 10 0.15 0.30
1000 36 33.5 satisfied 1.12 1.45 0.77 Example 11 0.10 0.30 1000 29
27.5 satisfied 1.08 1.43 0.76 Example 12 0.10 0.30 1000 29 26.5
satisfied 1.10 1.43 0.77 Example 13 0.20 0.30 1000 43 36.8
satisfied 1.08 1.47 0.73 Example 14 0.20 0.15 1000 43 39.8
satisfied 1.10 1.49 0.74 Example 15 0.20 0.50 1000 43 36.5
satisfied 1.08 1.44 0.75 Example 16 0.20 0.80 1000 43 44.5
unsatisfied 1.05 1.39 0.76 Comparative Example 17 0.20 0.30 980 43
38.5 satisfied 1.10 1.49 0.74 Example 18 0.20 0.30 980 43 45.0
unsatisfied 0.87 1.24 0.70 Comparative Example 19 0.25 0.40 1100 50
44.0 satisfied 1.10 1.48 0.74 Example 20 0.20 0.40 1100 43 37.0
satisfied 1.08 1.45 0.74 Example 21 0.10 0.40 1100 29 27.0
satisfied 1.08 1.45 0.74 Example 22 0.08 0.40 1100 26 24.0
satisfied 1.04 1.41 0.74 Example 23 0.20 0.40 1050 43 37.2
satisfied 1.08 1.44 0.75 Example 24 0.10 0.40 1050 29 27.4
satisfied 1.08 1.43 0.76 Example 25 0.08 0.40 1050 26 25.1
satisfied 1.04 1.40 0.74 Example 26 0.06 0.40 1050 23 22.1
satisfied 1.01 1.40 0.72 Example 27 0.20 0.50 1050 43 38.0
satisfied 1.10 1.48 0.74 Example 28 0.20 0.50 1050 43 38.5
satisfied 1.10 1.48 0.74 Example 29 0.20 0.50 1050 43 38.2
satisfied 1.10 1.48 0.74 Example 30 0.20 0.50 1050 43 37.5
satisfied 1.10 1.48 0.74 Example 31 0.20 0.50 1050 43 40.0
satisfied 1.01 1.32 0.77 Example 32 0.20 0.50 1050 43 40.5
satisfied 1.10 1.45 0.76 Example 33 0.20 0.50 1200 43 37.5
satisfied 1.10 1.45 0.76 Example
REFERENCE SIGNS LIST
[0123] 1 Multilayer electrical steel sheet [0124] 10 Inner layer
[0125] 20 Surface layer
* * * * *